It is well known that certain flight control surfaces, such as flaps, can be moved into and out of an airstream. The aerodynamic load on the flap is a function of the air speed and the flap deflection angle. When the flap is extended into the airstream, the aerodynamic load opposes the desired direction of flap movement. On the other hand, when the flap is retracted from an extended position, the aerodynamic load will “aid” the direction of flap movement.
Flaps have previously been actuated by electro-hydraulic servosystems. They have been actuated by three-phase DC servomotors acting through planetary gearing. One problem with this is that power must be continuously supplied to the motor for such time as the flap is extended into the airfoil surface. This represents a continuous power consumption, even though it is simply desired to hold the flap in a particular position for a period of time.
Accordingly, it would be generally desirable to reduce the power dissipated in an electric motor when it is desired to maintain a position under a constant load condition.